Letters to Nature

Nature 401, 152-155 (9 September 1999) | doi:10.1038/43646; Received 3 June 1999; Accepted 2 August 1999

Light-driven monodirectional molecular rotor

Nagatoshi Koumura1,2, Robert W. J. Zijlstra1, Richard A. van Delden1, Nobuyuki Harada2 & Ben L. Feringa1

  1. Department of Organic and Molecular Inorganic Chemistry, Stratingh Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
  2. Institute for Chemical Reaction Science, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan

Correspondence to: Ben L. Feringa1 Correspondence and requests for materials should be addressed to B.L.F. (e-mail: Email: B.L.Feringa@chem.rug.nl).

Attempts to fabricate mechanical devices on the molecular level1, 2 have yielded analogues of rotors3, gears4, switches5, shuttles6, 7, turnstiles8 and ratchets9. Molecular motors, however, have not yet been made, even though they are common in biological systems10. Rotary motion as such has been induced in interlocked systems11, 12, 13 and directly visualized for single molecules14, but the controlled conversion of energy into unidirectional rotary motion has remained difficult to achieve. Here we report repetitive, monodirectional rotation around a central carbon–carbon double bond in a chiral, helical alkene, with each 360° rotation involving four discrete isomerization steps activated by ultraviolet light or a change in the temperature of the system. We find that axial chirality and the presence of two chiral centres are essential for the observed monodirectional behaviour of the molecular motor. Two light-induced cis-trans isomerizations are each associated with a 180° rotation around the carbon–carbon double bond and are each followed by thermally controlled helicity inversions, which effectively block reverse rotation and thus ensure that the four individual steps add up to one full rotation in one direction only. As the energy barriers of the helicity inversion steps can be adjusted by structural modifications, chiral alkenes based on our system may find use as basic components for 'molecular machinery' driven by light.